`policy` argument to MIMEText constructor is too strict

[dkg]

0 dkg@bob:~$ cat test.py
#!/usr/bin/python3

from email.mime.text import MIMEText
from email.policy import SMTP

msg = MIMEText("this is the message\n",
               "plain", policy=SMTP)
print(msg, end="")
0 dkg@bob:~$ mypy --strict ./test.py 
test.py:7: error: Argument "policy" to "MIMEText" has incompatible type "EmailPolicy[EmailMessage]"; expected "Policy[Message[str, str]] | None"  [arg-type]
Found 1 error in 1 file (checked 1 source file)
1 dkg@bob:~$ 

email.mime objects can typically take a policy option, but the default is compat32, which can be found in the private email._policybase submodule. But there are other common EmailPolicy objects which are supposed to work there.

I'm not an expert in the python email module type choices, It looks to me like the type signature for this argument should be loosened up to be a union of these two types, at least. This probably goes for all the comparable email.mime constructors, not just MIMEText.

I ran into this on a debian system with mypy 1.15.0-5 and python3-typeshed 0.0~git20241223.ea91db2-1, with python 3.13.

[srittau]

Related PR (that will probably not fix this, but should be merged first, before a fix is worked on): #13532